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Biomedical subjects

R Bolli

Publications and source records attributed to R Bolli.

At least 73 records · Page 4Linked to original sources
PubMed1997

Preconditioning of human myocardium with adenosine during coronary angioplasty.

BACKGROUND: It is unknown whether adenosine can precondition human myocardium against ischemia in vivo. METHODS AND RESULTS: Thirty patients were randomized to receive a 10-minute intracoronary infusion of adenosine (2 mg/min) or normal saline; 10 minutes later, they underwent percutaneous transluminal coronary angioplasty (PTCA; three 2-minute balloon inflations 5 minutes apart). In control patients, the ST-segment shift on the intracoronary ECG was significantly greater during the first inflation than during the second and third inflations, consistent with ischemic preconditioning. In contrast, in adenosine-treated patients, there were no differences in ST-segment shift during the three inflations. The ST-segment shift was significantly smaller in the adenosine-treated group compared with the control group during all three inflations. The reduction in ST-segment shift afforded by adenosine during the first inflation (-72% versus first inflation in control subjects) was greater than that afforded by ischemic preconditioning in control subjects (-52% during the third versus first inflation). Measurements of chest pain score paralleled those of ST-segment shift. Adenosine had no effect on baseline regional wall motion as determined by quantitative two-dimensional echocardiography. Thus, intracoronary infusion of adenosine before PTCA rendered the myocardium remarkably resistant to subsequent ischemia. Judging from the intracoronary ECG, the protection provided by adenosine was even superior to that provided in control subjects by the ischemia associated with the first two balloon inflations. Infusion of adenosine had no major adverse effects in patients undergoing PTCA of the left anterior descending or circumflex arteries. CONCLUSIONS: Adenosine preconditions human myocardium against ischemia in vivo. Pretreatment with adenosine is remarkably effective (even more effective than ischemic preconditioning) and could be used prophylactically to attenuate ischemia in selected patients undergoing PTCA of the left anterior descending coronary artery. Whether adenosine can be safely infused into the right or the circumflex coronary artery in the presence of a temporary pacemaker remains to be established.

Adenosine↗
PubMed1997

Role of adenosine receptors in late preconditioning against myocardial stunning in conscious rabbits.

Conscious rabbits underwent six 4-min coronary occlusions interspersed with 4-min periods of reperfusion for 2 consecutive days (days 1 and 2 of stage I); 2 wk later, they underwent the same protocol (days 1 and 2 of stage II) except that they received either 8-(p-sulfophenyl)theophylline (SPT) on day 1 (group I, n = 5) or 2-chloro-N6-cyclopentyl-adenosine (CCPA) on the day before day 1 (group II, n = 6). In both groups I and II, on day 1 of stage I, systolic wall thickening (WTh) remained significantly depressed for several hours, indicating myocardial stunning; on day 2, however, the total deficit of WTh was approximately 50% less than on day 1 (P < 0.01), indicating the development of late preconditioning (PC) against myocardial stunning. Despite administration of SPT, in group I the deficit of WTh during stage II was 55% less on day 2 than on day 1 (P < 0.05). Similar results were obtained in three other rabbits treated with PD-115199 on day 1. In group II, pretreatment with CCPA during stage II failed to decrease the deficit of WTh on day 1. This study presents a new conscious rabbit model for studying myocardial stunning that is relatively inexpensive and technically less demanding than larger animal models. In this model, the development of late PC against myocardial stunning is not blocked by nonselective blockade of adenosine receptors with either SPT or PD-115199, nor is it induced by activation of adenosine A1 receptors with CCPA, indicating that adenosine receptors are not involved in the pathogenesis of this phenomenon.

Animals↗
PubMed1997

Late preconditioning against stunning is not mediated by increased antioxidant defenses in conscious pigs.

Previous studies in conscious pigs have demonstrated that a sequence of ten 2-min coronary occlusion/2-min reperfusion cycles renders the heart relatively resistant to myocardial stunning 24 h later [late preconditioning (PC) against stunning] by an unknown mechanism. Since oxygen radicals contribute importantly to myocardial stunning and since antioxidant enzymes have been reported to be upregulated 24 h after PC in dogs and rabbits, we tested the hypothesis that late PC against stunning is related to an increase in endogenous antioxidant defenses. Chronically instrumented conscious pigs underwent a sequence of ten 2-min coronary occlusion/2-min reperfusion cycles (preconditioned group, n = 11) or received no intervention (control group, n = 5). Twenty-four hours later, pigs were killed and the myocardial levels of Mn superoxide dismutase (SOD), Cu-Zn SOD, catalase, glutathione (GSH) peroxidase, GSH reductase, GSH, GSH disulfide, alpha-tocopherol, and ascorbate were measured. There were no differences in any of the enzymatic or nonenzymatic antioxidants between the ischemic and nonischemic regions in the preconditioned group or between the control and the preconditioned group. Thus, when a marked protection against stunning was present (24 h after PC), no alteration in antioxidant defenses was observed. These results indicate that, in conscious pigs, late PC against myocardial stunning is not mediated by increased endogenous antioxidant defenses, thereby refuting one of the major current hypotheses regarding this phenomenon.

Animals↗
PubMed1997

Nitric oxide triggers late preconditioning against myocardial infarction in conscious rabbits.

We tested the hypothesis that late preconditioning (PC) against myocardial infarction is triggered by the formation of nitric oxide (NO). Conscious rabbits underwent a 30-min coronary occlusion followed by 3 days of reperfusion. In group I (control group, n = 10), rabbits were not preconditioned, whereas in group II (n = 10), they were preconditioned 24 h earlier with a sequence of six 4-min occlusion/4-min reperfusion cycles. Myocardial infarct size (tetrazolium staining) was reduced by 50% by PC (28.6 +/- 3.2% of the risk region in group II vs. 56.9 +/- 5.9% in controls, P < 0.05). This reduction in cell death was associated with improved recovery of myocardial function [systolic thickening fraction (by sonomicrometry) at 3 days: 2.0 +/- 11.0% of baseline in group II vs. -20.0 +/- 2.8% in group I, P < 0.05]. Group III rabbits (n = 11) underwent the same protocol as group II except that the rabbits received the NO synthase inhibitor N omega-nitro-L-arginine (L-NNA, 13 mg/kg) before the PC ischemia. In these animals, infarct size did not differ significantly from that observed in control rabbits, indicating that L-NNA completely blocked the development of late PC against myocardial infarction. In group IV (n = 9), rabbits received L-NNA as in group III, but without the six occlusion-reperfusion cycles, and were subjected to the 30-min occlusion 24 h later. In this group, infarct size did not differ from that observed in controls, demonstrating that pretreatment with L-NNA, in itself, did not affect the extent of cell death. Taken together, these results indicate that, in the conscious rabbit, the development of late PC against myocardial infarction is triggered by the generation of NO during the PC ischemia. It is proposed that NO plays a key role in the delayed myocardial adaptation to ischemic stress.

Animals↗
PubMed1997

The early and late phases of ischemic preconditioning: a comparative analysis of their effects on infarct size, myocardial stunning, and arrhythmias in conscious pigs undergoing a 40-minute coronary occlusion.

The effectiveness of the late phase of ischemic preconditioning (PC) in protecting against myocardial infarction and the concomitant contractile dysfunction after sustained ischemia remains unclear. The early and late phases of PC have not been compared using the same protocol in the same experimental model; furthermore, the late phase of PC has not been assessed in the conscious state in a large animal preparation. The goal of this study was to directly compare the effects of early and late PC on myocardial infarct size and postischemic dysfunction in chronically instrumented, conscious pigs. Four groups of pigs were subjected to a 40-minute coronary occlusion followed by 3 days of reperfusion. Group 1 (n=7) served as control. Group 2 (n=6) was subjected to ten 2-minute occlusion/2-minute reperfusion cycles 25 minutes before the 40-minute occlusion (early PC). Groups 3 (n=7) and 4 (n=4) were subjected to 10 and 25 cycles, respectively, of 2-minute occlusion/2-minute reperfusion 24 hours before the 40-minute occlusion (late PC). Infarct size averaged 45.1+/-5.9% of the region at risk in control pigs, was reduced by 79% (to 9.4+/-3.2%) in group 2, but did not differ in groups 3 (33.3+/-4.8%) and 4 (38.8+/-8.2%) versus group 1. Power analysis demonstrated that there was an 80% probability of detecting a 40% decrease in infarct size in groups 3 and 4 versus group 1. The recovery of systolic wall thickening (measured with ultrasonic crystals) after the 40-minute occlusion was poor in groups 1, 3, and 4 but markedly enhanced in group 2 throughout the 3 days of reperfusion; this beneficial effect could have been due to limitation of infarct size, alleviation of stunning, or both. Thus, a series of ten 2-minute coronary occlusions had a profound (approximately 80%) early infarct-limiting effect, which was associated with a marked functional benefit. This protection, however, disappeared 24 hours later and could not be reinstituted by increasing the number of PC coronary occlusions to 25. The incidence and duration of ventricular tachycardia after reperfusion was not changed by either early or late PC; no conclusions could be drawn regarding ventricular fibrillation or ischemia-induced ventricular tachycardia, since these arrhythmias did not occur in control animals. Taken together, the present results demonstrate striking differences between the early and late effects of PC: In conscious swine subjected to a sustained coronary occlusion, a PC protocol that induces powerful protection during the early phase of PC fails to induce any protection during the late phase, indicating either that a late protective effect of PC does not exist or that, if it exists, it must be weaker than the early protective effect.

Animals↗
PubMed1997

Selective activation of A3 adenosine receptors with N6-(3-iodobenzyl)adenosine-5'-N-methyluronamide protects against myocardial stunning and infarction without hemodynamic changes in conscious rabbits.

To examine the cardioprotective role of A3 adenosine receptors during myocardial ischemia/reperfusion injury, we tested the effect of N6-(3-iodobenzyl)adenosine-5'-N-methyluronamide (IB-MECA), a potent and selective A3 adenosine receptor agonist, in models of myocardial stunning and infarction in chronically instrumented conscious rabbits. In phase I (studies of myocardial stunning), rabbits were subjected to six 4-minute coronary occlusions, each separated by 4-minute reperfusion periods, after which the recovery of systolic wall thickening was measured (ultrasonic crystals). In phase II (studies of myocardial infarction), rabbits were subjected to a 30-minute coronary occlusion followed by 3 days of reperfusion. In both phases, IB-MECA was administered as an intravenous bolus (100 micrograms/kg) 10 minutes before the first coronary occlusion. This dose of IB-MECA was determined in pilot studies to have no effect on heart rate, arterial blood pressure, or plasma histamine concentration in rabbits. In phase I, IB-MECA markedly improved the recovery of wall thickening after the six occlusion/reperfusion cycles, and this effect was sustained throughout the 5-hour observation period; the total deficit of wall thickening (a measure of the overall severity of myocardial stunning) was reduced by 68% (control, 129 +/- 16 arbitrary units, n = 7; IB-MECA, 41 +/- 6 arbitrary units, n = 6; P < .01). The protective effects of IB-MECA against stunning were completely blocked by pretreatment with the nonselective adenosine receptor antagonist 8-p-sulfophenyl theophylline or the specific protein kinase C inhibitor chelerythrine. In phase II, IB-MECA reduced myocardial infarct size by 61%; infarct size (tetrazolium staining) was 41 +/- 4% of the risk region in control animals (n = 8) and 16 +/- 6% in IB-MECA-treated animals (n = 8, P < .01). These results demonstrate that in conscious rabbits the A3 adenosine receptor agonist IB-MECA confers a powerful protection against both reversible (stunning) and irreversible (infarction) injury during acute myocardial ischemia and reperfusion by a protein kinase C-mediated pathway, suggesting that selective activation of A3 receptors is an effective means of protecting the ischemic myocardium without hemodynamic changes.

Adenosine↗
PubMed1997

Evidence that late preconditioning against myocardial stunning in conscious rabbits is triggered by the generation of nitric oxide.

Recent studies in conscious pigs and rabbits have demonstrated that a series of brief coronary occlusions renders the heart relatively resistant to myocardial "stunning" 24 hours later (late preconditioning [PC] against stunning). The mechanism of this powerful cardioprotective response is unknown. The goal of the present study was to test the hypothesis that the development of late PC against stunning is triggered by increased generation of NO during the first ischemic challenge. Conscious rabbits underwent a sequence of six 4-minute coronary occlusion/4-minute reperfusion cycles for 3 consecutive days (days 1, 2, and 3). On day 1, rabbits received either an intravenous infusion of the NO synthase inhibitor NG-nitro-L-arginine (L-NA, 13 mg/kg before the first occlusion) (group II, n = 10) or vehicle (group I [control], n = 10). In the control group, on day 1 systolic wall thickening (WTh) in the ischemic/reperfused region remained significantly depressed for 4 hours after the sixth reperfusion, indicating myocardial stunning. On days 2 and 3, however, the recovery of WTh improved markedly, so that the total deficit of WTh decreased by 60% on day 2 and 55% on day 3 compared with day 1 (P < .01). In the L-NA-treated group, the total deficit of WTh on day 1 was similar to that observed in the control group. On day 2, however, the total deficit of WTh was not significantly different from that observed on day 1 and was 132% greater than that observed in control rabbits on day 2 (P < .01). On day 3, the total deficit of WTh was 66% less than that noted on day 2 (P < .01). Thus, in L-NA-treated rabbits the sequence of six coronary occlusions and reperfusions performed on day 1 failed to precondition against stunning on day 2, but the same sequence performed on day 2 did precondition against stunning on day 3. Another group of rabbits (group III, n = 6) received L-NA on day 1 in the absence of ischemia and was subjected to the occlusion/ reperfusion sequence on days 2 and 3. In these animals, the total deficit of WTh on day 2 did not differ from that observed in control rabbits on day 1, indicating that administration of L-NA did not exacerbate the severity of myocardial stunning 24 hours later; therefore, the absence of late PC against stunning on day 2 in group II cannot be ascribed to a delayed deleterious action of L-NA on WTh. In conclusion, these results demonstrate that the NO synthase inhibitor L-NA completely blocks the development of late PC against myocardial stunning in conscious rabbits, indicating that NO generated as a result of the PC ischemia triggers the development of the cardioprotective response observed 24 hours later. NO is known to exert numerous biological actions resulting in rapid but transient physiological responses. The present observations support a novel pathophysiological paradigm in which NO also plays a key role in the delayed myocardial adaptations to ischemic stress, acting as a signaling step in the transduction pathway that leads to increased resistance to subsequent ischemic injury.

Animals↗
PubMed1997

Ischemic preconditioning induces selective translocation of protein kinase C isoforms epsilon and eta in the heart of conscious rabbits without subcellular redistribution of total protein kinase C activity.

Considerable controversy surrounds the role of protein kinase C (PKC) in ischemic preconditioning (PC). Previous studies have used pharmacological agents and/or measured total myocardial PKC activity; however, no information is available regarding the effects of PC on individual isoforms in vivo. We performed a comprehensive evaluation (using Western immunoblotting) of the expression and subcellular distribution of all 11 currently known PKC isoforms in the heart of conscious rabbits subjected to four different ischemic PC protocols known to induce early and/or late PC (one, three, or six cycles of 4-minute coronary occlusion [4'O]/4-minute reperfusion [4'R]; four cycles of 5-minute occlusion [5'O]/10-minute reperfusion [10'R]). Ten PKC isoforms (alpha, beta1/beta2, gamma, delta, epsilon, zeta, eta, iota, lambda, and mu) were found to be expressed in the rabbit heart. Quantitative immunoblotting demonstrated that as a subgroup, conventional PKCs (cPKCs) are more abundant than novel PKCs (nPKCs) (1445 versus 313 pg PKC/microg tissue protein, respectively) and that PKC alpha is the predominant isoform among the cPKCs (alpha, beta1, beta2, and gamma), representing 51% of this subgroup, and PKC epsilon is the most abundant among the nPKCs (delta, epsilon, zeta, and eta), accounting for 62% of this subgroup. None of the ischemic PC protocols examined caused appreciable changes in total PKC activity, in the subcellular distribution of total PKC activity, or in the subcellular distribution of PKC isoforms alpha, beta1/beta2, gamma, delta, zeta, iota, lambda, and mu. In contrast, all PC protocols caused significant translocation of PKC epsilon and PKC eta isoforms from the cytosolic to the particulate fraction. The particulate fraction of PKC epsilon increased in a dose-dependent fashion with the number of occlusion/reperfusion cycles performed, from 35+/-2% in the control group to 43+/-2% after one 4'O/5-minute reperfusion (5'R) cycle (P<.05), 52+/-2% after three cycles (P<.05 versus one cycle), and 66+/-3% after six cycles (P<.05 versus three cycles). The particulate fraction of PKC epsilon also increased, after four 5'O/10'R cycles, to 50+/-3% (P<.05 versus control). In contrast to PKC epsilon, the translocation of PKC eta was independent of the number of occlusion/reperfusion cycles performed. The particulate fraction of PKC eta increased from 67+/-3% in the control group to 84+/-2% after one 4'O/5'R cycle (P<.05), 84+/-2% after three 4'O/4'R cycles (P<.05), 86+/-3% after six 4'O/4'R cycles (P<.05), and 83+/-2% after four 5'O/10'R cycles (P<.05). When expressed as a percentage of control values, the increases in the particulate fraction of isoform epsilon were greater than those of isoform eta. The effects of 4'O without reperfusion were similar to those of one cycle of 4'O/5'R, indicating that 5'R did not attenuate isoform translocation. This is the first study to demonstrate PKC translocation after ischemic PC in vivo. The results indicate that in the conscious rabbit, ischemic PC causes selective translocation of the epsilon and eta isoforms without demonstrable changes in total myocardial PKC activity, implying that measurements of total PKC activity are not sufficiently sensitive to detect the involvement of PKC in PC. The results are consistent with the concept that the epsilon and eta isozymes play an important role in the genesis of ischemic PC in the conscious rabbit.

Animals↗
PubMed1997

The protective effect of late preconditioning against myocardial stunning in conscious rabbits is mediated by nitric oxide synthase. Evidence that nitric oxide acts both as a trigger and as a mediator of the late phase of ischemic preconditioning.

Seventy-four conscious rabbits undergoing a sequence of six 4-minute coronary occlusion/4-minute reperfusion cycles for 3 consecutive days (days 1, 2, and 3) were assigned to nine groups. In group I (controls, n = 8), the recovery of systolic wall thickening (WTh) after the sixth reperfusion was markedly improved on days 2 and 3 compared with day 1, indicating late preconditioning (PC) against myocardial stunning; the total deficit of WTh after the sixth reperfusion was reduced by 56% on day 2 and 50% on day 3 compared with day 1 (P < .01). Administration on day 2 of the nonselective NO synthase (NOS) inhibitor N omega-nitro-L-arginine (L-NA) (group II, n = 8) or of the selective inducible NOS inhibitors aminoguanidine (AG) (group IV, n = 8) and S-methylisothiourea sulfate (SMT) (group VI, n = 6) completely abrogated late PC against stunning on day 2. On day 3, the expected PC effect became manifest in all groups. Administration of L-NA, AG, or SMT on day 1 (groups III [n = 7], V [n = 6], and VII [n = 5], respectively) had no discernible effect on the deficit of WTh on day 1, indicating that these agents do not augment the severity of myocardial stunning in nonpreconditioned myocardium. In group VIII (n = 7), the abrogation of late PC by SMT on day 2 was completely reversed by the concomitant administration of L-arginine (595 mg/kg IV), indicating that it was not due to nonspecific NOS-unrelated actions. Administration of L-arginine alone on day 2 (group IX [n = 5]) had no effect on the deficit of WTh. Furthermore, administration of L-NA on day 1 (group III) prevented the appearance of the PC effect on day 2, whereas AG (group V) and SMT (group VI) did not, suggesting that the development of late PC on day 1 is triggered by the endothelial (type III) isoform of NOS. This study demonstrates that three structurally different NOS inhibitors (L-NA, AG, and SMT), given 24 hours after the PC ischemia, consistently abrogate late PC against myocardial stunning in conscious rabbits, indicating that this cardioprotective effect is mediated by the activity of NOS. The results obtained with AG and SMT specifically implicate the inducible (type II) isoform as the mediator of the protection on day 2. Previous studies have shown that NO triggers the development of late PC. The present results indicate that NO plays a dual role in late PC against stunning, acting initially as the trigger and subsequently as the mediator of the protection.

Animals↗
PubMed1997

[N-2-mercaptopropionyl-glycine improves recovery of myocardial stunning after reversible regional ischemia in conscious dogs].

In order to investigate the therapeutic effect of N-2-Mercaptopropionyl-glycine (MPG), a scavenger of hydroxyl radical, on postischemic myocardial dysfunction of 39 conscious unsedated dogs were undergone a 15 min occlusion of left anterior descending coronary artery followed by 48 hours of reperfusion. The treated dogs (n = 17) received an infusion of MPG (100 mg/kg.h) for 60 minutes (starting 15 minutes before occlusion) while the control dogs (n = 22) received normal saline. The result showed that there were no significant differences between the two groups in collateral blood flow determined by radioactive microsphere, occlusion vascular bed and hemodynamic variables. Systolic thickening fraction of ventricular wall (an index of regional myocardial function) was similar in both groups under baseline condition and during ischemia, whereas it (expressed as percent of baseline) was considerably greater in treated dogs at 2, 3, 4, 5, 6 hours of reperfusion. Much more significant recovery was observed in the dogs with collateral flow less than 10% in MPG group. The exponential regression analysis showed that the lower the collateral flow, the greater the recovery of function in treated dogs. It is concluded that MPG improves recovery of myocardial function after reversible regional ischemia, especially with lower collateral blood flow.

Animals↗
PubMed1996

Evidence for an essential role of reactive oxygen species in the genesis of late preconditioning against myocardial stunning in conscious pigs.

Conscious pigs underwent a sequence of 10 2-min coronary occlusions, each separated by 2 min of reperfusion, for three consecutive days (days 1, 2, and 3). On day 1, pigs received an i.v. infusion of a combination of antioxidants (superoxide dismutase, catalase, and N-2 mercaptopropionyl glycine; group II, n = 9), nisoldipine (group III, n = 6), or vehicle (group I [controls], n = 9). In the control group, systolic wall thickening (WTh) in the ischemic-reperfused region on day 1 remained significantly depressed for 4 h after the 10th reperfusion, indicating myocardial "stunning." On days 2 and 3, however, the recovery of WTh improved markedly, so that the total deficit of WTh decreased by 53% on day 2 and 56% on day 3 compared with day 1 (P < 0.01), indicating the development of a powerful cardioprotective response (late preconditioning against stunning). In the anti-oxidant-treated group, the total deficit of WTh on day 1 was 54% less than in the control group (P < 0.01). On day 2, the total deficit of WTh was 85% greater than that observed on day 1 and similar to that observed on day 1 in the control group. On day 3, the total deficit of WTh was 58% less than that noted on day 2 (P < 0.01). In the nisoldipine-treated group, the total deficit of WTh on day 1 was 53% less than that noted in controls (P < 0.01). On days 2 and 3, the total deficit of WTh was similar to the corresponding values in the control group. These results demonstrate that: (a) in the conscious pig, antioxidant therapy completely blocks the development of late preconditioning against stunning, indicating that the production of reactive oxygen species (ROS) on day 1 is the mechanism whereby ischemia induces the protective response observed on day 2; (b) antioxidant therapy markedly attenuates myocardial stunning on day 1, indicating that ROS play an important pathogenetic role in postischemic dysfunction in the porcine heart despite the lack of xanthine oxidase; (c) although the administration of a calcium-channel antagonist (nisoldipine) is as effective as antioxidant therapy in attenuating myocardial stunning on day 1, it has no effect on late preconditioning on day 2, indicating that the ability of antioxidants to block late preconditioning is not a nonspecific result of the mitigation of postischemic dysfunction on day 1. Generation of ROS during reperfusion is generally viewed as a deleterious process. Our finding that ROS contribute to the genesis of myocardial stunning but, at the same time, trigger the development of late preconditioning against stunning supports a complex pathophysiological paradigm, in which ROS play an immediate injurious role (as mediators of stunning) followed by a useful function (as mediators of subsequent preconditioning).

Animals↗
PubMed1996

Nisoldipine attenuates myocardial stunning induced by multiple coronary occlusions in conscious pigs and this effect is independent of changes in hemodynamics or coronary blood flow.

Recent studies suggest that calcium channel blockers attenuate reversible post-ischemic myocardial dysfunction (myocardial "stunning") in vivo. This beneficial effect, however, has been shown either in open-chest preparations, which are subject to the confounding influence of many unphysiological conditions, or in models in which treatment caused significant hemodynamic alterations. Furthermore, all of the studies have been conducted in the dog, and almost all of them have examined the effect of calcium antagonists after a single ischemic episode. The goal of the present investigation was to assess the effect of nisoldipine in a conscious pig model of repetitive ischemia, and to determine whether the drug exerts direct cardioprotection independent of hemodynamic changes. A total of 33 conscious pigs were used. Pigs underwent a sequence of 10 2-min coronary occlusions, each separated by 2 min of reperfusion, and were randomly assigned to a treated group (n = 11), in which nisoldipine was infused at a rate of 0.5 microgram/kg/min from 15 min before the first coronary occlusion till 30 min after the last reperfusion, and a control group (n = 12), which received vehicle. Results showed that there were no significant differences between the two groups with respect to ischemic bed size or hemodynamic variables throughout the experiment. Collateral blood flow to the ischemic regions was virtually nil in both groups. During the sequence of coronary occlusions, systolic thickening fraction in the ischemic region decreased similarly in the two groups. After the 10th reperfusion, however, the recovery of wall thickening was markedly enhanced in treated compared to control pigs, with the differences being statistically significant at 5, 15, and 30 min and 1, 3, 4 and 5 h. The total deficit of wall thickening after the 10th reperfusion (an integrative assessment of post-ischemic dysfunction) was 51% less in the treated compared with the control group (P < 0.001). This study demonstrates that nisoldipine markedly attenuates myocardial stunning after multiple ischemic episodes in conscious pigs, the improvement is evident immediately after the end of the ischemic episodes and is sustained throughout the recovery phase. This beneficial effect is independent of any favourable hemodynamic changes, and therefore indicates a direct cardioprotective action of nisoldipine.

Animals↗
PubMed1996

Production and characterization of a reconstituted high density lipoprotein for therapeutic applications.

A method is described for the large scale preparation of reconstituted high density lipoproteins (rHDL) suitable for therapeutic use. Apolipoprotein A-I (apoA-I was isolated from precipitates obtained by cold ethanol fractionation of human plasma. This process includes several steps for virus removal and virus inactivation, among them pasteurization. Reconstitution of lipoprotein particles was performed by cholate dialysis using soybean phosphatidylcholine as the lipid source. An apoA-I:lipid ratio of 1:150 (mol:mol) was obtained. Redissolved rHDLs were disc-shaped particles resembling nascent HDL, as assessed by electron microscopy. The method was optimized for low content of free apoA-I protein as well as the low concentration of free lipid. The product was stabilized by lyophilization in the presence of sucrose. In vitro studies show potential effects it the prevention of gram-negative septic shock and in the inhibition of atherosclerosis.

Apolipoprotein A-I↗
PubMed1996

In vivo spin trapping of nitric oxide generated in the small intestine, liver, and kidney during the development of endotoxemia: a time-course study.

Spin trapping of nitric oxide (NO.) in vivo in liver, small intestine, kidney, and plasma of intact rats was accomplished using diethyldithiocarbamate (DETC) administered intraperitoneally. DETC combines with Fe2+ to form (DETC)2-Fe and is an excellent trapping agent for nitric oxide. DETC distribution and uptake by the organs of interest was determined and the formation of the active trapping agent (DETC)2-Fe was assayed in the various organs and plasma. The capacity of this spin trap to capture NO. in vivo was demonstrated by administering sodium nitroprusside to the animals. The trapping procedure was then used to assess the course of NO. generation during a 6 h period in animals that had been treated with endotoxin. The rate of NO. generation/gram tissue was determined during the last 15 min of each time period. The results indicate that induction of nitric oxide generation begins earliest in the small intestine, then in the liver, and still later in the kidney and plasma. Nitric oxide production was most intense in the liver and was still increasing at the end of the experiment. Control animals receiving the spin trapping agent showed only little or no evidence of nitric oxide production except for the small intestine. The results show that induction of NO. generation caused by endotoxin begins at different times in different organs.

Animals↗
PubMed1996

Time course of late preconditioning against myocardial stunning in conscious pigs.

We have recently found in conscious pigs that a sequence of brief coronary occlusions induces severe myocardial stunning, but when the same sequence is repeated 24 hours later, the severity of stunning is markedly reduced (approximately 50%) ("late preconditioning against stunning"). As an initial step toward elucidating the mechanism and potential clinical significance of this powerful cardioprotective response, the present study was conducted to define the time course of late preconditioning against myocardial stunning. Conscious pigs underwent a sequence of ten 2-minute coronary occlusion/2-minute reperfusion cycles and then a second identical sequence at 6 hours (group I, n = 7), 12 hours (group II, n = 6), 24 hours (group III, n = 10), 3 days (group IV, n = 10), or 6 days (group V, n = 11) after the first. Systolic wall thickening (WTh) in the ischemic/reperfused region remained significantly depressed for at least 3 hours after the 10th reperfusion of the first sequence, indicating myocardial stunning. When the second sequence of coronary occlusions was performed 6 hours after the first (group I), the recovery of WTh was similar to the first. In contrast, when the second sequence was repeated 12 hours after the first (group II), the recovery of WTh was improved, though not consistently, and the total deficit of WTh decreased by 41% (P < .05) compared with the first sequence. When the second sequence was repeated 24 hours (group III) and 3 days (group IV) after the first, the recovery of WTh was substantially enhanced, with 52% and 49% reductions in the total deficit of WTh, respectively (P < .01 versus the first sequence). When the second sequence was repeated 6 days later (group V), the recovery of WTh was indistinguishable from the first sequence. Thus, late preconditioning against myocardial stunning requires > 6 hours to develop, lasts for at least 60 hours after its appearance (with the most effective protection present at 24 hours and 3 days), and disappears within 6 days after the preconditioning ischemia, a time course that is consistent with the synthesis and degradation of cardioprotective proteins. In view of its sustained duration, this endogenous cardioprotective mechanism is of potential clinical importance.

Animals↗
PubMed1995

Effect of the hydrophilic alpha-tocopherol analog MDL 74,405 on detection of hydroxyl radicals in stunned myocardium in dogs.

We have previously shown in dogs that the hydrophilic alpha-tocopherol analog, MDL 74,405, attenuates postischemic myocardial dysfunction ("stunning") and generation of free radicals as assessed with the spin trap alpha-phenyl N-tert-butyl nitrone (PBN). However, we could not discern whether this drug acts on primary radicals (such as hydroxyl radical [.OH]) or on secondary radicals. The goal of this study was to directly determine whether the beneficial effects of MDL 74,405 result from actions against .OH. Open-chest dogs undergoing a 15-minute coronary artery occlusion and 3 hours of reperfusion received an intravenous infusion of either saline solution (control group, n = 7) or MDL 74,405 (n = 6) starting 30 minutes before coronary occlusion and ending 60 minutes after reflow at a dose of 0.3 mg/kg/hr. Formation of .OH was estimated by the technique of aromatic hydroxylation of phenylalanine. Phenylalanine was infused intravenously, and the plasma concentrations of the hydroxylated products ortho-, meta-, and para-tyrosines (o-, m-, and p-tyr) in the coronary venous effluent and in the arterial blood were measured with high-performance liquid chromatography. In the control group a dramatic increase in the myocardial release of o-, m-, and p-tyr was observed immediately after reperfusion; the release of tyrosines peaked at 1 minute of reflow and continued up to 10 minutes after reperfusion. MDL 74,405 abolished the release of o-tyr throughout the first 10 minutes of reperfusion but had a less pronounced effect on the production of m- and p-tyr. These results demonstrate that MDL 74,405 is effective in inhibiting .OH-initiated reactions in the postischemic stunned myocardium in the dog, suggesting that the anti-.OH action of MDL 74,405 is an important mechanism of action of this antioxidant.

Animals↗